The Presence of a Barrier Between the Blood Stream and the Brain

The presence of a barrier between the blood stream and the brain is suggested by the observation that

A) all cells of the body are stained by a dye injected into the bloodstream.
B) injection of dye into the bloodstream stains all cells but those of the brain and spinal cord.
C) the gut is stained by a dye injected into the brain ventricles.
D) injection of dye into the ventricles stains all cells of the body.
E) most chemicals rapidly reach the brain after oral ingestion..